The invention relates to an electric motor device for powering a tool clamp, of the type comprising a casing of an electric motor the shaft of which is connected to the clamp, to control tools carried by articulated arms, opening them, closing them and clamping them onto a part, by a system of the through-the-motor type which converts the rotary motion of the shaft into translational motion of a mechanism operating the clamp, this motor being linked to a slaving device coupled to the rotor of the motor, these being themselves connected to a control variator.
The application might for example be a resistance welding clamp, the tools mentioned above being then constituted by spot welding electrodes. It might also be any other tool such as a riveting, clinching or punching machine in which the tools are clamped onto a part to be processed at a given moment. In the case of a welding clamp, this might for example be a clamp in which the arms carrying the electrodes are of the so-called xe2x80x9cCxe2x80x9d type or xe2x80x9cscissorsxe2x80x9d type, it being necessary in all cases, to control the movements of this clamp, whether a welding clamp or some other kind, to convert the rotation of the motor shaft, by a screw-and-nut system or similar, into translational motion of a mechanism operating the clamp. This type of electric motor power, easier to slave, is tending to replace the provision of power by hydraulic or pneumatic jacks. The principle and the advantages of devices of this type have been indicated in particular in French patent no. 85 12239 on behalf of the applicant, describing a numerically controlled resistance welding machine.
The function of the control variator mentioned above is to supply current to the motor to cause it to rotate during the dynamic phases of movement of the tool-carrying arms (opening or closing the clamp) and, in the static phase, to cause it to apply a torque converted by this motion conversion system into a force clamping the tools onto the part, for example a sheet of metal to be welded.
As to the slaving device already mentioned, of the analogue (resolver) or digital (encoder) type, this is coupled to the rotor of the motor and its function is to provide the control variator with information on the position and speed of the rotor of the motor, thus slaving it.
As regards the production of such machines, there are several concepts for providing motor power, namely using a system for converting rotary motion into translational motion of the type separate from the motor or of the through-the-motor type. For the sake of simplicity, it will be assumed that screw-and-nut systems are used, but it goes without saying that the principles of the invention will remain valid for any other type of motion conversion system, using a rack and pinion, for example, or other means.
According to the concept of the separate type, shown as an example in FIG. 1, the axis of the screw 1, engaged with a nut 2 capable of translational motion in the body 3 of the device, is parallel to the axis 4a of the electric motor 4. The clamp operating mechanism, not shown, is designated 5 and has a motion-transmitting link to the nut 2 via the part 5a. Consequently, the output shaft 6 of the motor 4 must be connected to the head of screw 1 by some kind of system for transmitting rotary motion, for example using gears or a toothed belt and pulleys, the system as a whole being designated 7. This design means that there is easy access to the head of the screw 1 from the end casing 8 after the closure plug 9 is removed from the casing. It is then possible to insert an appropriate key into a splined hole in the screw 1 to turn it manually, the motor 4 being stationary. This means that the screw 1 can be turned by hand, for example to make an adjustment to the clamp or to the electrodes or other tools. It will be noted that the device 10 for slaving the motor 4, located at the end of the motor casing, in no way hampers these operations.
On the other hand, this type of construction does have the disadvantages of requiring a large number of parts, being of considerable weight and size on a welding machine, and of being costly.
According to the concept of the through-the-motor type, i.e. using a through-the-motor screw, which does not have the same disadvantages and which is shown as another example in FIG. 2, the screw-and-nut system is directly integrated with the motor: here, the nut 2 is capable of rotational motion and is therefore directly integral with the rotor 11 of the motor 4, the stator of which is designated 12. The screw 1, engaged with this nut and capable of axial translational motion in the motor 4, has a projecting end 5 constituting the clamp operating mechanism. Here it will be noted that, contrary to the previous case, the device 10 for slaving the motor 4, still located at the end of the motor shaft and which may itself be masked by a printed circuit board 10a, prevents any access to the end of the rotor 11, and therefore prevents it being turned manually when the motor 4 is stationary, in order to turn the nut 2 and cause the screw 1 to move forward.
To eliminate this disadvantage, consideration might be given to changing the position of the device 10 for slaving the motor, away from the end of the shaft, offsetting it relative to the latter and linking the slaving device to the rotor of the motor by means of a gear wheel and pinion or a pulley and toothed belt assembly. The end of the shaft of the motor 4 would then again be accessible to be rotated manually, but this would still have the disadvantages of complexity of construction (additional parts), an increase in size and a higher manufacturing cost.
The aim of the invention is to eliminate all these disadvantages of the prior art, and therefore to obtain convenient access to the motor shaft to rotate it and thus move the clamp operating mechanism in translation manually, achieving this at lower cost and without increasing either the size or the weight of the equipment.
To this end, according to the invention, a device such as is defined at the outset is of the type using a through-the-motor system for converting rotary motion into translational motion and is characterised in that, the slaving device coupled to the rotor of the motor being arranged at the end of the motor shaft, the shaft is fitted with a gear wheel which can be operated from the outside, for rotating it manually, through an opening in the casing offset with respect to the motor shaft.
The gear wheel in question may be a bevel gear, and the axis of the opening may form a certain angle with the axis of the motor, for example an angle of 90xc2x0.
According to a variant, the gear wheel is cylindrical and meshes with a cylindrical pinion which can be operated through the opening, and the axis of the opening can then be parallel to the axis of the motor.
The gear wheel mentioned will advantageously be rotated by a key, and the end of this key may have a set of teeth which can engage with the gear wheel.
As a variant, the motor casing contains a set of teeth which can be operated through the opening and can be rotated by the key and at the same time be made to engage with the gear wheel on the end of the shaft, the set of teeth and gear wheel being disengaged from each other by the action of a spring or of inertia when the key is withdrawn.
According to another variant, provision may also be made for the motor casing to contain a set of teeth which can be operated through the opening and can be rotated by the key, this set of teeth being permanently engaged with the gear wheel mentioned.
Of course, all the gears involved may be of any appropriate type, for example spur, helical or angle, or a rack and worm screw may be used.